The present invention relates generally to data networks, and more particularly to a method of verifying connectivity between nodes in a communications network.
A communications network is a group of nodes interconnected by a transmission medium. The term “node” relates to any device that shares frames of data with other nodes in the network. Devices that may make up a node are computers, printers, scanners, etc. A node may also be a telephone, a television, a set-top box for televisions, a camera or other electronic sensing or communication device. Any device that can send and/or receive frames of data with other devices via a communication medium may be a node for purposes of the present invention.
The transmission medium that links each node in a network is equally one of a diverse family of media. Common media used include unshielded twisted pair (e.g. phone wire, CAT-5 cabling), power lines, optical fiber, coaxial cable and wireless transmission media. The operations that each individual node performs in order to access data from, and transmit data to, the rest of the network may be logically broken down into seven layers according to the ISO Open Systems Interconnection (OSI) seven-layer network model, which is also referred to as the “network stack,”. The seven layers, from the bottom to the top are: 1) the PHYSICAL layer, 2) the DATA LINK layer, 3) the NETWORK layer, 4) the TRANSPORT layer, 5) the SESSION layer, 6) the PRESENTATION layer, and 7) the APPLICATION layer. FIG. 1 illustrates the ISO seven-layer reference model.
The PHYSICAL layer, or physical link layer, is concerned with transmission of unstructured bit stream traffic over physical media, and relates to the mechanical, electrical, functional, and procedural characteristics to access and receive data from the physical medium. The DATA layer, sometimes referred to as the data link layer, provides for the reliable transfer of information across the physical link. It is concerned with sending frames, or blocks of data, with the necessary synchronization, error control, and flow control. The NETWORK layer separates the uppermost layers from the transmission and switching technologies used to connect nodes. It relates to establishing, maintaining, or terminating connection between nodes.
The TRANSPORT layer relates to reliability and transparency in data transfers between nodes, and provides end-to-end error recovery and flow control. The SESSION layer provides control to communications between applications, and establishes, manages, and terminates connections between cooperating applications. The PRESENTATION layer provides independence to the application processes from differences in data syntax or protocols. Finally, the highest layer, the APPLICATION layer, provides access to the OSI environment for users. Much more has been written about the benefits and distributed functionality of such an arrangement of layers and need not be recounted here.
In frame-based networks, there are two fundamental models or topologies: 1) broadcast/multipoint networks, where all nodes are physically attached to the same network medium, and use a single, shared channel and frames transmitted on the network are visible to all nodes; and 2) point-to-point networks, where pairs of nodes are connected to each other with communication channels which are not connected to any other nodes on the network. Frames transmitted on one channel are not visible to nodes on other channels unless the frames are retransmitted onto the other channels by a node that is connected to multiple channels. Each channel may use a separate segment of the network medium, or multiple channels may share a single segment using e.g., Frequency Division Multiplexing or Time Division Multiplexing techniques. One common example of such a point-to-point network topology is that used for IEEE 10BaseT 802.3 networks, with network nodes connected via point-to-point Category 5 unshielded twisted pair cable, using multi-port devices called hubs to retransmit frames received from one network segment to all other segments.
Each node in either type of network has within it a device that permits the node to send and receive data frames in the form of electrical, electromagnetic, or optical signals. The device is conventionally a semiconductor device implementing the PHYSICAL layer of the network connectivity, and the medium access control (MAC) portion of the DATA layer of network connectivity. For effective interconnectivity, it is important to periodically check to make sure the communication channels, or media, between nodes are functional. When all or part of the media is not functional, data may be lost and the network is rendered useless.
Methods of verifying connectivity of communication channels between nodes in a multi-node network exist. In point-to-point networks, such as those promulgated by IEEE 802.3, SMDS, and HDSL standards, the verification methods operate on the individual point-to-point communication channels between two nodes only. They do not provide verification for connectivity between multiple nodes. They are also not adaptable to broadcast networks.
Connectivity verification methods for broadcast methods exist as well. These methods operate at the highest layer of the network stack, the APPLICATION layer. They are designed to test and monitor overall network operation, thereby consuming large amounts of bandwidth of the shared medium. They are also not designed to identify problems at the lower network layers, such as connectivity problems at the PHYSICAL layer, separately and independently from problems at the higher layers, such as problems with the TRANSPORT layer at a node.
Verification methods at the APPLICATION layer suffer from even further shortfalls. To implement them, the network must have at least one high-level system containing a complex software application with connectivity verification capability. This software application also requires that other nodes contain some sort of embedded software, at a minimum to communicate with the software application to confirm connectivity results. Further, by placing verification functionality at the APPLICATION layer, the verification information is required to go from the APPLICATION layer at one node to the NETWORK layer at each of the other nodes, and then back again in order to complete the verification process. This requires that all of the layers through which the verification information passes must operate properly, or the verification will fail.
Therefore, a method and system are needed for verifying connectivity between nodes in both broadcast and point-to-point networks and that operate at lower levels of the network stack, while minimizing verification traffic on communication channel, and while operating separately and independently of higher-layer hardware and software in each node. The present invention provides such a method and system.